Dental alloys employed in the porcelain-fused-to-metal processing technique may be classified into several groups, including gold based, palladium based, cobalt based, and titanium based. One of the most important criteria in deciding which alloy to use is the cost of the alloy. The cost of the alloy is dependent upon the commodity prices of the alloy components. For example, in March 2007, the cost of the major components of each the above alloys was:
Gold $730 per Troy ounce,
Palladium $350 per Troy ounce, and
Cobalt $2.23 per Troy ounce.
The economic advantage of the base metal cobalt is obvious, but the functional characteristics of base metal alloys do not compare with those of gold based or palladium based alloys, and for this reason they are not generally used in dental products. For example, in general cobalt base metal alloys are more difficult to cast, grind and bond to porcelain.
There have been numerous attempts to improve the functional characteristics of cobalt based alloys through the addition of gold and the platinum group metals (the platinum group metals consist of platinum, palladium, rhodium, iridium, osmium and ruthenium). Examples from the prior art are listed in Table 1, below.
TABLE 1SUMMARY OF PRIOR ARTAuthorUS Pat. #CommentsProsen4,253,869Describes a cobalt chromium alloy with7 to 15 wt. % ruthenium.Prosen4,255,190Describes a cobalt chromium alloy with7 to 15 wt. % ruthenium with gallium.Zwingmann4,382,909Describes a cobalt chromium alloy thatwith 1 to 70 wt. % palladium.Prasad4,459,263Describes a cobalt chromium alloy with5 to 15 wt. % ruthenium.Vuilleme6,613,275Describes a cobalt chromium alloy with0.5 to 4 wt. % gold.Prasad6,656,420Describes an alloy with 25 to 60 wt. %gold and up to 2 wt. % rutheniumbalance cobalt.Prasad6,756,012Describes a cobalt chromium alloy withup to 20 wt. % platinum or palladium,up to 10 wt. % gold and up to 6 wt. %ruthenium.
In each case, some improvement in the functional characteristics of the base metal alloy has been achieved through the addition of gold and/or the platinum group metals. However, to date no successful commercial formulation of a cobalt based high palladium content alloy has been obtained that is consistent with the American Dental Association (ADA) guidelines for “noble” alloys required for use in dental products (i.e. alloys having at least 25% gold or palladium).
For example, although the Zwingmann patent discloses a wide range of possible cobalt based palladium alloys, most of these have strong magnetic properties. Likewise, Ivoclar Vivadent, Inc. manufactures a cobalt based high palladium content alloy sold under the tradename Calisto CP, which has a composition of 56 wt. % cobalt, 10 wt. % chromium, 26.2 wt. % palladium, 3 wt. % tungsten and 2 wt. % gallium. However, this alloy is also strongly magnetic and therefore poses potential problems for use in dental applications. Specifically, magnetic dental inserts and appliances can make it difficult if not impossible to use advanced imaging techniques such as Magnetic Resonance Imaging (MRI) on patients. In addition, such magnetic materials can cause false positives when individuals are scanned during security check-ins (for example, at airports). Accordingly, a need exists for improved cobalt based “noble” dental alloys that possess non-magnetic properties.